As a couple of people above have already mentioned, the next logical step for Nintendo in my opinion is to bring together their handheld and TV console platform and release a fusion device. I.e. a fully portable gamepad (albeit sleeker and a bit smaller) that is HD, and can be played through the TV as well as via some kind of dongle. I expect Nintendo will leverage the technology they've developed with the Wii U and gamepad to provide a low latency experience (just in the opposite direction, from handheld to TV), and release a console with a similar level of power to the Wii U in maybe late 2016/early 2017.
I think they really need to do this in order to pool their resources, rather than split them between the handheld console and TV one, as they are now. This is crucial really, due to the lack of 3rd party support.
There are two issues that Nintendo will have to overcome though. The first is price- can they release that type of device at a consumer-friendly price point? It could be difficult. The second issue is backwards compatibility. Traditionally, Nintendo have been strong on this, compared to Sony and Microsoft. But, with the Wii U being disc-based, and most consumers still buying physical games at this point, how this will be done I don't know.
What I do know though is that I would buy it day one.